1. Field of the Invention
The present invention relates generally to integrated circuits, and more specifically, to an integrated circuit for implementing a inductorless electroluminescent panel driver.
2. Background of the Invention
Electroluminescent (EL) panels are in common use as backlights for keyboards and displays. Recent uses of EL panels include wrist watches, cellular telephone displays and keyboards, notebook computers and personal digital assistants (PDAs). In order to produce illumination from an EL panel, an alternating high voltage power supply is required. An EL panel driver includes a high voltage power supply, and a mechanism for switching the high voltage power supply output to produce a high voltage output of alternating polarity for connection to the EL panel.
Traditionally, an integrated circuit controlled for implementing an EL panel driver circuit contains an oscillator, a high voltage power supply and a switching circuit coupled to the oscillator and the high voltage power supply for creating the alternating high voltage output for connection to the EL panel.
The high voltage power supply in an integrated circuit EL panel driver typically includes connections for either an inductor or a transformer to convert a low voltage input power supply to a high voltage that is then coupled to one or more terminals of the integrated circuit, which include a flyback switch transistor terminal and a terminal for coupling the high voltage DC output to the switching circuit that alternates the voltage supplied to the EL panel.
With the high density integration requirements present in devices such as cellular telephones and notebook computers, and in devices having very small packages such as wristwatches, it is desirable to produce a single integrated circuit solution with a minimum of external components and terminals. However, it is impractical to incorporate inductors or transformers within an integrated circuit package.
Therefore, it would be desirable to provide a inductorless apparatus and method for driving EL panels that may be incorporated within a single integrated circuit package.
The above objective of providing a inductorless apparatus and method for driving EL panels is accomplished in an integrated circuit including a high voltage power supply and a switching circuit for producing an alternating high voltage output from the high voltage power supply. The high voltage power supply includes a plurality of charge pump circuits for generating the high voltage power supply output. The high voltage power supply may also include a multi-stage charge pump to reduce voltage loss associated with driving charge pump circuits from a low voltage power supply, which results in a lesser number of overall charge pumps required to achieve a the voltage level required to drive the EL panel.
The foregoing and other objectives, features, and advantages of the invention will be apparent from the following, more particular, description of the preferred embodiment of the invention, as illustrated in the accompanying drawings.